The risk of infection increases as greater numbers of patients are treated with more intensive cytotoxic and immunosuppressive therapy. At the Baltimore Cancer Research Program an intensive infection surveillance program assesses the ongoing infectious disease status of the patients and the Program as a whole. From this data base have grown appropriate basic infection control policies and specific research approaches including evaluation of laminar air flow rooms, simpler means of air filtration and reverse isolation, oral nonabsorbable antibiotics and techniques to prevent axillary and oral infections. Trimethoprim/sulfamethoxazole and nalidixic acid, both absorbable antibiotics, are being evaluated as a means of suppressing the aerobic gram-negative flora while preserving colonization resistance. These programs are enforced by the infection control nurse. Ketoconazole, an imidazole derivative with good activity against Candida sp., will be included in the oral antibiotic regimens and compared to the antifungal currently in use: nystatin.